Thanks for the responce. I just unscrewed the choke on my M4 on the side of the choke it reads Steel Shot OK-M- XXX. According to the manual it's a Modified choke, if it has X it's a full choke if it has XX it's a Improved Modified choke, if it has XXXX it's a Improved Cylinder choke and if it has XXXXX it's a skeet choke. Plus it has three notches on top of the choke letting me know I have a Modified choke, two notches Improved Modified choke etc. I still don't know if I can use 00 buck or slugs.